1. Field of the Invention
The invention relates to the technical field of the crop protection agents.
More specifically, it relates to a thermodynamically stable crystal modification of 2-({2-chloro-4-(methy Isulfonyl)-3-[(2,2,2-trifluoroethoxy)methyl]phenyl}carbonyl)cyclo-hexan-1,3-dione of the formula
(hereinbelow referred to as tembotrione), to processes for its preparation and to its use as herbicide.
2. Description of Related Art
It is known that some organic compounds can occur in only one crystal structure while others (so-called polymorphs) can occur in various crystal structures, see, for example, J. Bernstein, R. J. Davey, J. O. Henck, Angew. Chem. Int. Ed., 1999, 38, 3440-3461. Thus, EP 1 314 724 A1 discloses two crystal structures of the herbidically active compound sulcotrione.
Tembotrione, which is known, for example, from WO 00/21924 (example No. 3 in table 1), has herbicidal properties and is suitable for preparing crop protection compositions used for weed control. However, it has been found that the tembotrione preparable in accordance with the disclosure of WO 00/21924 is not suitable for preparing user-friendly presentation forms. User-friendly presentation forms are, for example, suspension formulations in which tembotrione is present finely ground in solid form. In tests in practice, it has been found that, in suspension formulations, tembotrione preparable in accordance with the disclosure of WO 00/21924 leads to crystal growth and, as a consequence thereof, to agglomeration and precipitation, such that the suspension formulation becomes unusable. The crystal growth may occur spontaneously or over a relatively long period of time and is unpredictable.